请教关于触摸屏的校正

首先采样周围4个点
采样程序如下：
#include

typedef struct {
 unsigned short pressure;
 unsigned short x;
 unsigned short y;
 unsigned short pad;
} TS_EVENT;

static TS_EVENT ts_event;
static int ts;

int main()
{
ts = open ("/dev/ts", 0);
if (ts < 0) {
fprintf (stderr, "2410: Can not open touch screen!\n");
return 0;
}

while(1)  
{
if(read(ts,&ts_event,sizeof(TS_EVENT)))
{
printf("X=%d,Y=%d,Pressure=%d \n",ts_event.x,ts_event.y,ts_event.pressure);
}      

}
}

在板子上运行时，对于同一个点采样的显示结果却太不一样了
如下所示：
/bin $ ./readpos
X=127,Y=0,Pressure=33049
X=47,Y=0,Pressure=36633
X=1,Y=0,Pressure=9737
X=255,Y=0,Pressure=41
X=1,Y=0,Pressure=9
X=1,Y=0,Pressure=1545
X=254,Y=0,Pressure=64057
X=255,Y=0,Pressure=1065

有人知道是怎么回事么，谢谢